1. Field of the Invention
The present invention relates to a conductive roller, and more particularly to a conductive roller preferably which is preferably used as a transfer roller in an image-forming apparatus including OA equipment such as an ink jet printer, a laser printer, an electrostatic copying machine, a facsimile apparatus, and the like and an automatic teller machine (ATM).
2. Description of the Related Art
It is necessary for the conductive roller such as a transfer roller, a driving roller, a developing roller, a charging roller, and the like to have an appropriately stable electric resistance value.
As conventional methods of imparting conductivity to the conductive roller of this kind, the following two methods are conventionally used: In one known method, an electroconductive polymer composition containing a conductive filler such as powder of metal oxides, carbon black or the like in a polymer thereof is used. In the other known method, an ionic-conductive polymer composition such as urethane rubber, acrylonitrile butadiene rubber, epichlorohydrin rubber or the like is used.
In the case where the electroconductive polymer composition is used for a conductive roller, there is a region in which the electric resistance of the conductive roller changes rapidly owing to a slight change of an addition amount of the conductive filler. Thus it is very difficult to control the electric resistance of the conductive roller. In addition, because it is difficult to uniformly disperse the conductive filler in the polymer, the electric resistance value has variations in the circumferential and widthwise directions of the conductive roller.
The electric resistance value of the conductive roller using the electroconductive polymer composition depends on a voltage applied thereto. In particular, in the case where the carbon black is used as the conductive filler, the electric resistance value of the conductive roller depends greatly on the voltage applied thereto.
Further when the electroconductive polymer composition contains a very large amount of the conductive filler such as the carbon black, it is difficult to mold the electroconductive polymer composition.
The conductive roller using the electroconductive polymer composition has the above-described problems. Recently, a high-quality image forming technique including a digital image processing technique and color image processing technique has remarkably progressed. Thus there is a tendency that the ionic-conductive polymer composition is used preferentially to the electroconductive polymer composition.
Mostly the ionic-conductive polymer composition is used as a vulcanized rubber composition to form the conductive roller. But the vulcanized rubber composition is not thermoplastic and cannot be recycled.
When a conventional ionic-conductive agent is used, it is difficult to effectively decrease the electric resistance of the conductive roller. When a large amount of the ionic-conductive agent is contained in the polymer composition, bleeding occurs and mechanical properties of the composition composing the conductive roller such as the compression set, hardness, and the like deteriorate.
To overcome the above-described problem, the present inventors developed a conductive polymer composition which has rubber-like durability, elasticity, and flexibility, and resin-like moldability, is recyclable, and has a low electric resistance.
More specifically, as disclosed in Japanese Patent Application Laid-Open Nos. 2004-51829 (patent document 1) and 2004-269854 (patent document 2), the present inventors proposed the conductive dynamically crosslinked thermoplastic elastomer composition which is formed by adding the polymer having the ether or ester structure and the anion-containing salt having the fluoro group and the sulfonyl group to the elastomer composition in which the crosslinkable rubber or/and the thermoplastic elastomer are dynamically crosslinked and dispersed in the thermoplastic resin or/and the thermoplastic elastomer. They also proposed the conductive roller composed of the conductive dynamically crosslinked thermoplastic elastomer composition.
The above-described conductive roller does not have any problems when it is used in the neighborhood of a normal temperature. However, the hardness of the conductive roller is a little high. Thus when the conductive roller is used in a low-temperature environment as a transfer roller, the conductive roller causes the adhesiveness of toner to paper to decrease. Thereby there is a fear that a defective image is generated because the toner is not exactly transferred to the paper. Thus the above-described dynamically crosslinked thermoplastic elastomer composition leaves improvement for keeping the hardness thereof low in the low-temperature environment.
Patent document 1: Japanese Patent Application Laid-Open No. 2004-51829
Patent document 2: Japanese Patent Application Laid-Open No. 2004-269854